This kind of system is mentioned in a Japanese patent application No. 61(1986)-6061. This application discloses a system having a fail-safe means. The fail-safe means consists of a generation means which is included in a microcomputer as a program, and is operable for generating a pumping signal which has a constant frequency or duty ratio, and a driving means which judges whether the frequency or duty ratio of the pumping signal from the generation means is normal or not, and the driving means is operable for driving an actuator to a "safety side" in the abnormal case.
In a Japanese patent Laid-open application No. 60(1985)-205373, the same kind of system is mentioned. This application discloses a system having a fail-safe means in the same way. The fail-safe means consists of a generation means which is included in a microcomputer as a program and is operable for generating a pumping signal which has a constant frequency, and a resetting means which judges whether the frequency is normal or not, and the resetting means is operable for resetting the microcomputer in the abnormal case.
In these prior art systems, the generation means is included in a program of the microcomputer. For example, a step for setting a pumping flag as "1" is set to a place which is surely passed in a main routine of the microcomputer, and in a timer interrupt of the microcomputer, the pumping signal is turned over when the pumping flag is set as "1". If the movement of the microcomputer is normal, then the pumping signal is turned over at a constant interval, and therefore the abnormality of the microcomputer can be detected.